Warm an oven-safe skillet over medium-high heat. Then, toss in the onions and ground beef. Sauté for three to five minutes or until the meat is brown and the onions looks tender.
Pour the cream cheese into the skillet. Then, follow the green chilis and taco seasoning. Sauté and mix the cream cheese to completely coat the ground beef.
Simultaneously, prepare the oven by preheating it to 350F.
Remove the skillet from the heat source and allow it to cool for a minute. Then, top the meat and cream cheese mixture with corn chips and sprinkle the shredded cheese on top of the corn chips.
Place the skillet in the preheated oven and bake the taco casserole for 20 minutes.
Remove and allow it to cool for a minute. Then, top it shredded tomato and lettuce.
Finally, garnish the taco casserole with sour cream and salsa.